R：如何创建多个分割数据矩阵？

Question

I am using trade data (FAO) which I would like to turn into matrices (per Item and Year). Therefore I've done a split:

# import is the original df
import_YI <- split(import, list(import$Item, import$Year))
import_YI_lap <- lapply(seq_along(import_YI), function(x) as.data.frame(import_YI[[x]])[, 1:11]) 

and the data looks like this (you can find test data at the end) :

[[1]]
RC         PC       Item       Year    Value   
Argentina  Chile    Almonds    1996    1108  
Algeria    Spain    Almonds    1996    1  
....
[[2]]
....
[[3]]
....
[[n]]

I used the cast function (below) to create a matrix for almonds in 2012:

# import_almonds2012 is a test subset from import df (with import values for almonds in 2012)
RCPC <- cast(RC ~ PC, data =import_almonds2012, value = "Value")

Now my question: how can I do matrices of all Items/Years (~100 Items and 17 years!!) from the import_YI_lap df? My problem is that I don't know (1) how to operate the levels/ojects in this df ( [[1]], [[2]]... ). Or there a better way to split data or to save the splited df into objects? And (2) how to create all the needed matrices without coping thousend lines of code. Loops? If yes, how??

here a test-dataset:

import<- data.frame(RC=c("DE", "IT", "USA"),
                PC = c("BRA", "ARG"),
                Item = c("Almonds", "Apples"),
                Year = c(1996,1997,1998),
                Value = c(1,5,3,2,8,3))

import_YI <- split(import, list(import$Item, import$Year))
import_YI_lap <- lapply(seq_along(import_YI), function(x) as.data.frame(import_YI[[x]])[, 1:5])
import_YI_lap

Answer 1

没有数据很难进行测试，但是您可以尝试以下操作：

do.call(rbind,import_YI_lap)